The present application is directed to piezoelectric diaphragm structures, and more particularly to piezoelectric diaphragm structures having optimized diaphragm displacement characteristics.
Piezoelectric diaphragm structures are implemented as actuators which move upon being supplied with electrical energy, and as sensors (e.g., pressure, movement, strain sensors) where diaphragm movement is translated into electrical signals. One particular implementation of a diaphragm structure is as part of an ejection unit used to eject drops such as ink, biofluid or other material from a fluid reservoir. In a desire to improve the efficiency of such ejection units, there is a continuing effort to reduce the voltages required for ejection, create ejector heads with higher nozzle density, and to reduce costs. Reaching these goals requires an improvement in the ejector efficiency, including an efficient diaphragm structure. In particular, an improved diaphragm structure will operate at a lower voltage, increase the volume displacement per volt, while also maintaining a low overall area and retaining adequate diaphragm stiffness.
A previous diaphragm structure is set out in U.S. Pat. No. 4,045,695 to Itagaki et al. which describes an electro-acoustic transducer comprising a flexible film of piezoelectric material, at least one electrode being provided on one side of the film, and a plurality of electrodes being provided on the other side of the film to form a piezoelectric diaphragm. The diaphragm is imparted with a locally distinct resiliency and tension, and is implemented in a loudspeaker, making it possible to improve acoustic characteristics, particularly in a high-frequency range.
A second patent, U.S. Pat. No. 4,170,742, also to Itagaki et al., focuses on the specifics of the diaphragm structure layout, including a paddle-shaped first electrode in the center and a “C” second electrode exterior the first.
U.S. Pat. No. 5,663,505 to Nakamura discloses a pressure sensor, which includes a vibrator having a diaphragm valve for detecting pressure. A plurality of circular electrodes are located on planes of first and second piezoelectric bodies wherein the various electrode portions interact causing a radial vibration which acts to expand and contract the device in opposite directions. Operation of the upper and lower electrodes are intended to cause radial motion, without motion out of plane.
These references do not particularly discuss a design directed to optimizing the deflection of the diaphragm which increases the deflection per voltage applied. They also do not, among other concepts, define a structure, used in conjunction with the poling and actuation operations, which achieve an optimized diaphragm operation.